How Does Metformin Cause Erectile Dysfunction?

Erectile dysfunction is a common condition experienced by 18% of men¹ over age 20 in the United States. While many factors can contribute to the development of impotence, certain medications, like metformin, can impact penile blood flow and testosterone levels. 

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What is metformin?

Metformin is a commonly prescribed medication that works to lower blood glucose levels. It increases insulin sensitivity within the body, allowing insulin, naturally occurring or administered during therapy, to work more efficiently to control blood sugar.

What are the uses of metformin?

Metformin is often prescribed to treat type 2 diabetes. Patients with type 2 diabetes are insulin-resistant; insulin doesn’t work effectively in their bodies. Insulin is a hormone produced by the pancreas to control blood sugar levels after you eat. 

When we eat carbohydrate-rich foods, they’re broken down into glucose (a form of sugar), which then enters the bloodstream. High blood glucose levels trigger the pancreas to release insulin, which signals cells in the body to absorb glucose from the blood and convert it to energy. 

In patients with type 2 diabetes, the body becomes resistant to insulin, meaning that insulin is still released by the pancreas but is ineffective at removing glucose from the bloodstream. 

Metformin increases the body’s insulin sensitivity and improves glucose absorption into cells without affecting insulin production. 

Other medications, such as sulfonylureas, can cause hypoglycemia (low blood sugar) due to their effect on insulin production. Metformin is generally considered a safer choice for diabetic patients and is often used in combination with other drugs.

In addition to treating type 2 diabetes, metformin is used off-label to treat gestational diabetes. It also shows potential as an anti-oncogenic (anti-cancer) therapy. 

Diabetes and erectile dysfunction

Does diabetes cause erectile dysfunction?

Diabetes is a metabolic disease that affects insulin production and function. When the body doesn’t have enough insulin, or the insulin created doesn’t function properly, blood glucose levels can’t be controlled. 

This often leads to excess blood glucose (hyperglycemia). Over time, hyperglycemia can damage the heart, eyes, nerves, and blood vessels. Individuals with diabetes often have multiple complications, such as increased cardiovascular risk, obesity, and hypertension. 

A lesser-known side effect of diabetes in men is erectile dysfunction. Studies have shown that erectile dysfunction is 3.5 times more common² in men with diabetes than in men without it, and more than half of men with diabetes may be affected. 

The causes of erectile dysfunction in diabetic patients vary, with physical, hormonal, and psychological complications impacting sexual function. 

Physical complications from diabetes often include damage to blood vessels and nerves. Hyperglycemia is the primary cause of macrovascular and microvascular complications in individuals with diabetes. 

This includes larger blood vessels affecting the heart and smaller vessels like the ones found in penile tissue. 

Tight regulation of these penile blood vessels is needed to allow adequate blood flow to enter and remain in the penis to create and maintain erections firm enough for sexual intercourse. 

When a man is sexually aroused, the endothelial cells of the blood vessels produce nitrous oxide, which acts as a signal to cause the vascular smooth muscle of the corpora cavernosa to relax, increasing blood flow into the penis. 

Veno-occlusion prevents outward blood flow and keeps the blood there to maintain the erection. Hyperglycemia can affect penile blood vessels through:

  • damaging endothelial cells and inhibiting the production of nitrous oxide; this prevents subsequent vasodilation (widening of blood vessels) and blood flow into the penis

  • plaque buildup in penile blood vessels (atherosclerotic luminal narrowing), which can reduce blood flow into the penis

Peripheral neuropathy (nerve damage) is associated with advanced diabetes. It can cause erectile dysfunction due to the lack of sensory impulses from the penis and reduced contractile force of the penile muscles, making it harder for the muscles to hold the blood in the penis.

Can diabetes worsen erectile dysfunction?

In general, the incidence of erectile dysfunction increases with age for most men. However, men with diabetes experience erectile dysfunction earlier than men without it. 

Men with diabetes may notice that the problem worsens over time as their disease progresses. Erectile dysfunction in men with diabetes may be a warning sign for more adverse conditions, such as cardiovascular disease. 

Diabetes and erectile dysfunction share common risk factors associated with diseases that cause endothelial disruption. 

Visceral adiposity (excessive visceral fat), common in overweight diabetic men, can cause inflammation and decreased levels of nitrous oxide, leading to erectile dysfunction.

Diabetes can also affect hormone regulation, which plays a significant role in sexual desire and erectile dysfunction. 

Testosterone is an important hormone that regulates sex drive. It also contributes to penile endothelial and smooth muscle function. Men with long-term diabetes are more likely to have subnormal levels of testosterone³ (hypogonadism), which can contribute to erectile dysfunction.

Erectile dysfunction can be triggered through emotional and cognitive processes, and it’s known that depression can lead to reduced libido and a decrease in the frequency of attempted sexual intercourse. 

Depression is twice as likely to occur in individuals with diabetes than in those without it. In diabetic patients, depressive symptoms are correlated with erectile dysfunction. This issue is nuanced, as it may be that depression has an impact on sexual function, but a reduction in sexual satisfaction may also contribute to depression. 

Unfortunately, erectile dysfunction can also be a side effect of some medications used to treat complications of diabetes. Diuretics used to treat hypertension, such as thiazides and beta-blockers, can cause erectile dysfunction due to decreased forceful blood flow to the penis. 

Metformin and erectile dysfunction

Can metformin cause erectile dysfunction?

Metformin is commonly used to increase insulin sensitivity in diabetic patients; however, insulin isn’t the only hormone metformin can affect. 

Metformin inhibits a key enzyme in testosterone synthesis, reducing circulating testosterone. 

Lower testosterone can affect sex drive and penile blood flow, contributing to erectile dysfunction. Other diabetic medications, such as sulfonylureas, which aren’t as commonly prescribed, may not have the same effect on testosterone.

How does metformin help erectile dysfunction?

In contrast with the information provided above, some studies⁴ report that metformin alleviates erectile dysfunction in diabetic patients. With insulin resistance, high insulin levels remain in the body, leading to inflammation and nitrous oxide depletion. 

Metformin improves insulin sensitivity and reduces insulin levels, relieving hyperglycemia. Controlling hyperglycemia minimizes the damage it causes to the blood vessels and nerve cells in penile tissue. 

Treatment with metformin can:

  • increase blood flow to the penis by endothelium-dependent vasodilation

  • improve regulation of sympathetic nerve activity

Is metformin safe to use to treat erectile dysfunction?

Metformin is generally a safe medication for diabetic patients. It’s effective at controlling blood glucose levels and preventing hyperglycemia, which, over time, can lead to damaged penile tissues and cause erectile dysfunction. 

However, using metformin to treat nonvascular or neuropathic erectile dysfunction is not recommended. Recent studies have also indicated metformin can reduce testosterone levels in men.

Several medications are generally well-tolerated by diabetic patients, including Viagra (sildenafil) and Cialis (tadalafil).

Combining medication with a healthy lifestyle is essential, as erectile dysfunction can worsen as diabetes progresses. Anyone taking metformin and noticing signs of worsening erectile dysfunction should talk to a doctor about other treatment options.

The lowdown

Erectile dysfunction is a common complication in diabetic men and can be caused by physical, hormonal, and emotional dysfunctions. Hyperglycemia can cause numerous complications in penile tissue, and controlling diabetes is vital to prevent severe symptoms. 

While metformin is the standard treatment for diabetic patients, it may have unintended side effects, including lowered testosterone, that can contribute to erectile dysfunction. However, it can generally be taken safely alongside medications specifically for treating erectile dysfunction, such as Viagra and Cialis.

  1. Prevalence and risk factors for erectile dysfunction in the US (2007)

  2. High prevalence of erectile dysfunction in diabetes: A systematic review and meta-analysis of 145 studies (2017)

  3. Update: Hypogonadotropic hypogonadism in type 2 diabetes and obesity (2011)

  4. Effects of metformin on endothelial health and erectile dysfunction (2017)

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